William Petty, 1st Marquess of Lansdowne, KG, PC (2 May 1737 – 7 May 1805), known as The Earl of Shelburne between 1761 and 1784, by which title he is generally known to history, was an Irish-born BritishWhig who was the first Home Secretary in 1782 and then Prime Minister 1782–1783 during the final months of the American War of Independence. He succeeded in securing peace with America and this feat remains his most notable legacy. He was also well known as a collector of antiquities and works of art

When Pitt was made Prime Minister in 1766 Shelburne was appointed as Southern Secretary, a position which he held for two years. He departed office during the Corsican Crisis and joined the Opposition. Along with Pitt he was an advocate of a conciliatory policy towards Britain's American Colonies and a long-term critic of the North Government's measures in America. Following the fall of the North government Shelburne joined its replacement led by Lord Rockingham. Shelburne was made Prime Minister in 1782 following Rockingham's death with the American War still being fought. Shelburne's government was brought down largely due to the terms of the Peace of Paris which brought the conflict to an end which were considered excessively generous because they gave the new nation control of vast trans-Appalachian lands. Shelburne however had a vision of long-term benefit to Britain through trade with a large and increasingly prosperous United States, without the risk of warfare over the western territories.

After he was forced from office in 1782 at age 45, he permanently lost his power and influence. Shelburne lamented that his career had been a failure, despite the many high offices he held over 40 years, and his undoubted abilities as a debater. He blamed his poor education—although it was as good as most peers—and said the real problem was that "it has been my fate through life to fall in with clever but unpopular connections." Historians, however, point to a nasty personality that alienated friend and enemy alike. Biographer John Cannon says "His uneasiness prompted him to alternate flattery and hectoring, which most of his colleagues found unpleasant, and to suspiciousness....In debate he was frequently vituperative and sarcastic." Success came too early, and produced jealousy, especially when he was tagged as an upstart Irishman. He never understood the power of the House of Commons, or how to deal with its leaders. He advocated numerous reforms, especially free trade, religious toleration, and parliamentary reform. He was ahead of his time, but was unable to build an adequate network of support from his colleagues who distrusted his motives. In turn he distrusted others, and tried to do all the work himself so that it would be done right.